earth science changes to earth''s surface

Earth’s Crust Earth is covered by a rock layer called the crust.. Rocks slowly break into smaller pieces.. Physical WeatheringIn physical weathering, rock breaks into smaller pieces of t

Trang 1

by Marcia K Miller

Scott Foresman Science 4.9

Genre Comprehension Skill Text Features Science Content

Nonfi ction Compare and

Contrast

• Labels

• Captions

• Diagrams

• Glossary

Earth’s Surface

ISBN 0-328-13883-5

ì<(sk$m)=bdiidi< +^-Ä-U-Ä-U

Earth Science

Scott Foresman Science 4.9

Genre Comprehension Skill Text Features Science Content

Nonfi ction Compare and

Contrast

• Labels

• Captions

• Diagrams

• Glossary

Earth’s Surface

ISBN 0-328-13883-5

ì<(sk$m)=bdiidi< +^-Ä-U-Ä-U

Earth Science

Trang 2

deposition

earthquake

epicenter

erosion

fault

landform

landslide

volcano

weathering

What did you learn?

1 What can cause a landslide?

2 What makes magma rise inside a volcano?

3 Why do earthquakes happen at faults?

4 Erosion and deposition are two forces that change landforms Explain in your own words what each force does Include details from the book to support your answer.

weathering and chemical weathering alike? How are they different?

Illustration: 14 Alan Male

Photographs: Every effort has been made to secure permission and provide appropriate credit for

photographic material The publisher deeply regrets any omission and pledges to correct errors called to its

attention in subsequent editions Unless otherwise acknowledged, all photographs are the property of Scott

Foresman, a division of Pearson Education Photo locators denoted as follows: Top (T), Center (C), Bottom

(B), Left (L), Right (R) Background (Bkgd)

Opener: ©Hubert Stadler/Corbis; Title Page: ©Chris Reynolds and the BBC Team-Modlemakes/DK

Images; 4 ©AP/Wide World Photos; 5 ©Jack Dykinga/Getty Images; 7 (T) ©Richard Bickel/Corbis, (B)

©Owaki-Kulla/Corbis; 8 ©Paul A Souders/Corbis; 10 ©Dave G Houser/Corbis; 13 (TR, CR) ©Gary

Rosenquist; 15 ©George Hall/Corbis

ISBN: 0-328-13883-5

protected by Copyright and permission should be obtained from the publisher prior

to any prohibited reproduction, storage in a retrieval system, or transmission in any

form by any means, electronic, mechanical, photocopying, recording, or likewise For

information regarding permissions, write to: Permissions Department, Scott Foresman,

1900 East Lake Avenue, Glenview, Illinois 60025.

3 4 5 6 7 8 9 10 V010 13 12 11 10 09 08 07 06 05

Changes to Earth’s Surface

Trang 3

How does Earth’s

surface wear away?

Earth’s Crust

Earth is covered by a rock layer called the crust The crust

is underwater in the ocean

Earth’s crust has many natural features Each one is called

a landform Landforms are many sizes and shapes Plains

are flat landforms on low ground Plateaus are flat landforms

on high ground Peninsulas are landforms that stick out into

water Valleys and canyons are also landforms

3

Some landforms develop quickly Others take a long time

A mountain may take millions of years to form Rocks rolling downward can change it quickly Think of how a flood moves soil from one place to another Think about dust that blows across empty, unplanted fields

How Weathering Affects Landforms

Landforms are always changing Rocks slowly break into

smaller pieces This process is called weathering Water, ice,

and temperature changes can cause weathering Chemicals and living things cause weathering too

Trang 4

Physical Weathering

In physical weathering, rock breaks into smaller pieces of the same kind of rock Water can cause physical weathering Flowing water carries small bits

of soil and sand These bits scrape against rocks to wear them down

Ice also causes physical weathering Rain or melting snow can get into cracks in rocks If this water freezes, it turns into ice The ice pushes against the cracks The cracks become deeper This process can repeat until the rock finally splits

Changes in temperature can also weather rocks A rock’s surface grows larger when it gets hot Its surface shrinks when it gets cold All this changing may weaken the rock

Living things can also cause weathering Have you seen plants living in the cracks of rocks? As plants and roots grow, they can split the rocks

4

Weathering changed the rock known as the Old Man of the Mountain in New Hampshire In 2003 the rock broke off and fell.

Chemical Weathering

In chemical weathering, rock breaks into smaller pieces But the material that the rock is made of also changes

Different materials can be formed when chemicals come in contact with rock Carbon dioxide, a chemical in the air, mixes with rainwater and forms a weak acid When it rains, this acid lands on the rock It combines with rock material and forms

a new chemical Over time, the new chemical breaks the rock into smaller pieces

Chemicals can come from animals and plants These chemicals can cause weathering So can people and their activities

As water moves, it weathers rock and carries it to new places.

5

Trang 5

How do weathered

materials move?

Effects of Erosion

Erosion is the process of moving weathered rock Water, ice,

gravity, and wind can cause erosion

Rain can wash away loose rock material into a stream The

stream may carry that material far away

Over time, water running downhill carves grooves into the

land These grooves become canyons or valleys

Waves pound against cracks in rocks that are at the shore

Pieces of rock break off and are carried away As the shore

erodes, new landforms, such as beaches, will appear

Millions of years ago, huge ice sheets, called glaciers, covered

parts of Earth A glacier slowly slides along a thin layer of water

below it, wearing away rock Even small glaciers can rip rocks

apart and carry the pieces far away

Deposition

Wind and water carry bits of rock and soil from one place

to another Deposition is the laying down of pieces of Earth’s

surface This may happen slowly or very quickly

When water moves slowly, big pebbles in the water sink first Then smaller bits, such as sand, sink Finally the smallest pieces

of soil, called silt, fall to the bottom Rivers deposit material where they meet the ocean This deposit forms a fan-shaped landform called a delta

Wind can carry only small bits of rock In deserts, the wind deposits sand in mounds called sand dunes Wind will keep shaping the dunes

Trang 6

Gravity and Landslides

No place on Earth is completely flat The force of gravity

pulls all objects from high places to lower ones Gravity causes

loose material to roll downhill Bits of rock and soil may move

slowly, only a little at a time But at times they move very

quickly Heavy rains or earthquakes can loosen material that

is on a steep hill or slope Gravity then pulls this loose material

downward A landslide is the quick downhill movement of

great amounts of rock and soil Buildings, trees, and other large

objects may be swept down the slope with the sliding soil

8

Gravity and Avalanches

The rapid movement of objects down a slope can occur in cold areas as well An avalanche is fast-moving snow and ice that race down a mountain Strong winds, earthquakes, and explosions can cause avalanches People try to stop avalanches from happening They may clear snow before it builds up too much Landslides and avalanches can cause terrible damage, especially on large mountains

9

Trang 7

Controlling Erosion and Deposition

Erosion and deposition often take place in areas with few

trees or plants Trees and plants help keep wind and water from

eroding rock and soil

People have found ways to slow the effects of erosion They

grow plants on the sides of hills Roots hold soil in place Plant

leaves keep some of the rain from washing soil away Farmers

whose fields are on a hill can plow them into steps, called

terraces Rain forms puddles on the steps instead of washing

soil downhill Crops can then soak up more water

11

Erosion can be a problem along the seashore as well Waves that pound against the shore carry away material, such as sand People build barriers to prevent this Barriers stop waves from eroding sand and rock Barriers also help protect nearby buildings and roads

People can reduce deposition They can dig away deposits from waterways This helps ships pass through the water more easily

Terraces slow the movement of water running downhill.

Trang 8

How can Earth’s surface

change rapidly?

Volcanoes

A volcano is a

landform It can

cause a rapid

change to Earth’s

surface Hot rock,

called magma, has

partly melted into liquid

Gases push the magma up A

volcano forms at a weak spot in

Earth’s crust

A volcano erupts when magma boils onto

the surface Lava is magma that has come out of a

volcano Lava is still red hot

Pressure can build so much that the gases in the

magma explode Lava, gases, and ashes burst out

of openings called vents Not all volcanoes erupt

so wildly Magma oozes up and slowly flows out

of some volcanoes A bowl-shaped area, or crater,

may form around the volcano’s main opening

13

Effects of Eruptions

When volcanoes erupt, they form ash and new rock Ash from the eruption of Mount St Helens in 1980 flew more than

24 kilometers (15 miles) into the air It covered nearby cities It killed trees and animals

Active and Dormant Volcanoes

An active volcano erupts often or shows signs that it will erupt Kilauea in Hawaii began its latest eruption in 1983 It is still actively erupting

A dormant volcano has not erupted for a long time Mount Rainier in Washington has not had a big eruption in more than

500 years If it erupted, it could melt nearby glaciers This could cause flooding and landslides

An extinct volcano no longer erupts Mount Kenya in Africa

is one of many extinct volcanoes in the world

The 1980 eruption of Mount St Helens sent rock and ash into the air.

Trang 9

Earth’s Moving Plates

Earth’s crust rests on a layer called the upper mantle

These layers form huge moving pieces called plates

The Cause of Earthquakes

A fault is a break or crack in rocks where Earth’s crust can

move Rocks may get stuck along a fault The plates keep

moving They press on the rocks that are stuck If the pressure

becomes strong enough, the rocks break The plates shift

quickly An earthquake is the sudden movement that makes

Earth’s crust shake

The focus is the underground spot where the plates shift and

the earthquake begins The epicenter is the point on Earth’s

surface above the focus The most damage is usually near the

epicenter Energy from an earthquake moves in waves

Epicenter Focus

Fault

15

Effects of Earthquakes and Volcanoes

Many places on Earth have earthquakes and volcanoes In

1815 Mount Tambora in Asia erupted Ash darkened the sky

Less sunlight reached Earth This caused snow to fall in the northeastern United States in June

In 1883 Krakatoa erupted in Indonesia This volcano caused huge waves called tsunamis in Earth’s oceans Earthquakes can also cause tsunamis Tsunamis can lead to landslides

Two plates meet in California along the San Andreas Fault

Many earthquakes happen along this fault Most are small

Some are very powerful

Weathering, erosion, and deposition change Earth’s landforms So do landslides, earthquakes, and volcanoes

Earth’s surface will always be changing

Earthquakes can cause great damage.

Trang 10

Glossary

after erosion